This application is related to and claims priority from Japanese Patent Application No. 2000-379761, filed on Dec. 8, 2000.
The present invention relates to a color filter to be used for a liquid crystal display unit capable of color display. The present invention relates also to a color liquid crystal display unit provided with said color filter, and more particularly, to a color liquid crystal display unit having improved display quality and increased brightness of light passing through the color filter from the back light for liquid crystal.
Display units, typified by liquid crystal display units, to display character and image information are available in a variety of types capable of color display. A common way to realize the color display is to use a color filter.
The conventional color filter consists of a glass substrate and color patterns formed thereon. The patterns are colored in red (R), green (G), and blue (B) with a pigment or dye. The color filter of this type selectively transmits light in a specific wavelength region and absorbs (or screens) light outside the specific wavelength region. This leads to the disadvantage that the transmittance of light through the color filter is low.
For example, in the case of an RGB color filter, the filter for blue color absorbs light in the wavelength region corresponding to red color and green color in the incident white light and transmits blue color. This causes more than two thirds of the amount of incident light to be lost.
A color filter to tackle the above-mentioned problem was disclosed in Japanese Patent Laid-open No. 202118/1999. As schematically shown in FIG. 1, this color filter consists of a glass substrate 4, two filter layers 2,3, and a flattening layer 1. The first filter layer 3 is laminated on that side of the glass substrate 4 from which light 11 emerges. The first filter layer consists of plural wavelength converting segments 3R, 3G, and 3B for red, green, and blue colors, respectively. The second filter layer 2 is laminated on that side of the first filter layer from which light emerges. The second filter layer consists of plural filter segments 2R, 2G, and 2B. The flattening layer 1 is intended to make flat the two layers laminated on top of the other.
The wavelength converting segments 3R convert light in the wavelength in the range from near ultraviolet to green into light in the wavelength region of red. The wavelength converting segments 3G convert light in the wavelength in the range from near ultraviolet to blue into light in the wavelength region of green. The wavelength converting segments 3B convert light in the wavelength in the range from near ultraviolet into light in the wavelength region of blue.
The liquid crystal display unit provided with the above-mentioned wavelength converting filter has the following disadvantage. In addition to the respective filter segments (2R, 2G, 2B) for red, green, and blue, it is essential to form the wavelength converting segments (3R, 3G, 3B) that convert the wavelength of incident light corresponding to the respective colors. This leads to an increase in steps for the production of color filter and also leads to a decrease in productivity of color filter.
Moreover, it is also necessary to form the segments comprising the color filtering layer by several steps after the wavelength converting layer has been formed. The severe heat history in these steps affects the segments comprising the wavelength converting layer underneath, which tends to deteriorate the function of the wavelength converting layer.
There is a need to address the above-mentioned problems. It is desirable to provide a color filter which has a high transmittance for incident light. It is further desirable to provide a color liquid crystal display unit capable of display with high brightness.
In accordance with an aspect of the invention, a color filter comprises a laminated structure having a substrate layer, color filter layer comprising plural filter segments, and a wavelength converting layer. The wavelength converting layer is co-extensive with the color filtering layer and comprises a material having the property of producing emergent light comprising a first range of frequencies in response to receiving incident light comprising a second range of frequencies.
In accordance with another aspect of the invention, a color filter comprises a laminated structure having a substrate layer, a color filtering layer comprising plural color filter segments, a first wavelength converting layer comprising plural first and second wavelength converting segments, and a second wavelength converting layer co-extensive with the color filter layer. The first wavelength converting segments produce first emergent light having a first range of wavelengths greater than a first wavelength value in response to receiving a first portion of incident light having wavelengths less than the first wavelength value. The second wavelength converting segments produce second emergent light having a second range of wavelengths greater than a second wavelength value in response to receiving a second portion of the incident light having wavelengths less than the second wavelength value. The second wavelength converting layer is a single layer of material which produces third emergent light having a third range of wavelengths greater than a third wavelength value in response to receiving a third portion of the incident light having wavelengths less than the third wavelength value.
In accordance with still another aspect of the invention, the foregoing aspects of the color filter are incorporated in a liquid crystal display device comprising a pair substrates. Disposed between the pair of substrates are a liquid crystal layer, a layer of transistor elements, and the foregoing described color filter.